Hello @David Mills ,
This error typically pertains to issues with permissions or network configurations. Temporary server congestion or network-specific issues could also trigger these errors, even if no changes were made to the network or account permissions
Try resetting your Hosts file to its default settings or accessing the service via an alternative network to see if the issue persists. You can find more details here: https://answers.microsoft.com/en-us/msoffice/forum/all/microsoft-365-defender-action-center-error-approve/b7efac4a-0be8-45e6-b9a9-69a89ad04170
I also saw that other users who encountered this error have seen it resolve itself, so it might just have been caused by network issues or congestion.
I hope this answers your question.
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If you have further questions, kindly leave a comment and I will get back to you.